- Author: Ben Faber
So I got an email with an attached set of photos showing a number of 18 month avocado trees that had broken at the ground line in a wind storm. It looked something like an incompatibility between scion and rootstock, since below the graft union the rootstock girth was substantially smaller than the scion. The problem is, I'd never heard of this between ‘Hass' and ‘Dusa' and the combination has been around for at least 15 years in trials.
So it was time to go out to the orchard and see the setting in which the trees had failed. And there was the answer. All of the trees had been planted too deeply. The trunk sleeves had been buried and the graft union was below grade and had been infected by disease organisms. The crown roots are the most active physiologically and that union area is a weak spot. Burying it encourages disease and a weak union.
The trees had been planted with an auger and over time the trees had settled into the soft earth and had been buried. The first time I had ever seen something like this was in Guatemala and Costa Rica. There growers had created these massive 3 x 3 X 3 foot holes and amended them 50% with compost. And over time, the trees had settled as the compost decomposed and the unions were covered with dirt. Occasionally you see people moving too fast when they are planting and this shows up in a few trees, not usually a whole orchard.
The lesson here, is that if you are going to err on plant depth, plant high. A few exposed roots won't hurt, and the settling problem doesn't become a problem. Of course it's best to plant just right.
Broken Trunks
The Buried Avocado Graft Union
- Author: Ben Faber
I am amazed how such a simple procedure can go so wrong. For avocado and citrus growers, it’s time to think about planting in the spring. And every spring and summer I get called out to diagnose trees that are failing. It often turns out that the trees have been planted too deeply. There are various ways of killing a tree, such as digging a hole too deeply and then backfilling. When the ground settles, it settles around the root collar and the tree suffocates. Or installing a dry root ball and then not irrigating soon enough. Or adding fertilizer to the planting hole which burns the roots. One of the major problems of lack education and supervision of the planting crew. Don’t assume that everyone knows how to plant a tree.
Deep planting can result in death of woody plants either because they rot in moisture saturated soils or they dry out. In either case, the symptoms are similar: wilting, sunscald or burnt leaves, lack of growth, leaf drop and eventual death of leaves, shoots and branches. Root balls planted below grade cause several problems at establishment. Since native soil surrounds the ball, there is an immediate problem with and interface between the two soil textures. Most container media are lighter than bulk soil, which is done to make sure there is adequate drainage in the nurse. When these soil-free media are planted in soil which is of a heavier texture, the interface does not allow the water to enter the root ball.
When trees are planted too deeply, they are much more subject to fungal cankers and other pathogens that can girdle the stem, killing it and all above ground parts. Planting slightly higher than grade will prevent this. Just look for the color, textural change between the roots and stem and dig the hole no deeper than the root ball to prevent settling. Newly planted trees can’t draw water from bulk soil, not until the roots move out into the soil will they be able to absorb water. Also planting cannot be rushed, because that’s when errors in planting occur.
- Author: Gary S. Bender
Since our last article on high-density avocados appeared in Topics in Subtropics we have had a lot of questions from growers concerning the cost of installation of such a grove. We have also had a lot of interest from potential winegrape growers who think this might be the way to go given that wine-grapes use about 25% of the amount of water per acre compared to avocados. For higher quality wines growers use less water, but harvest lower pounds/acre.
I am currently advising a student at Cal State San Marcos who is doing a cost study for removing an avocado grove and installing a winegrape planting in San Diego County. Hopefully we will have an article on that in the near future.
We don’t have a lot of experience in high density avocados but we will try to show some costs to help you decide.
Clearing an older grove can get expensive. In a study we did in 2010 we found that it cost $40/tree to cut a tree down, haul the cut wood down to a firewood stack and haul to small branches to a chipper. The old stump is usually killed with a herbicide and left in place to rot. So, just to remove a tree at 109 trees/acre may cost $4,360 per acre.
For our high density planting we will be planting Hass avocados grafted on Dusa rootstock. We are using this rootstock because it appears from several trials to be a good rootstock for resistance to avocado root rot in the well-draining hillside soils in San Diego County.
The current price is about $30/tree (plus or minus). For a 10’ x 10’ spacing we would plant about 435 trees per acre, this would be an initial cost of $13,500/acre. We are not calculating the cost of a grove road installation, and we are assuming that the entire acre would be planted.
Planting cost: digging, planting, wrapping and staking trees takes about 15 minutes per tree. This includes carrying the tree to the hole. At 435 trees per acre, this would take about 109 hrs. At $14/hr, this would cost $1526/ac. Stakes (435) at $2.25/stake would cost $979/ac.
The irrigation system installation would cost $2,660/ac. This is based on an entire system being installed in a 20 acre block, divided by 20 to get the cost per acre.
There are quite a few other costs that you can see from our complete avocado cost study, but these basic costs will get the trees in the ground (Table 1).
Table 1. Basic costs for the installation of a high density avocado grove. |
|
Trees (Hass on Dusa rootstock) |
$13,500 |
|
|
Planting (digging, planting and wrapping) |
$1,526 |
|
|
Stakes |
$979 |
|
|
Irrigation system |
$2,660 |
|
|
Total |
$18,665/acre |
If you are thinking about planting 10 acres, then you would need $186,650 in the bank to get the trees in the ground. There will be some shifting of costs because this study does not include clearing or building of grove roads, and with grove roads you will be planting less numbers of trees/acre.
Will you make more money in the long run? That is the question we are trying to answer with our high density trial in Valley Center.
Reference
Bender, G.S. and E. Takele. 2010. A guide to estimate compensation for loss of a single avocado tree. University of California Cooperative Extension county publication AV 606.
Takele, E., Bender, G.S., and M.Vue. 2011. Avocado sample establishment and production costs and profitability analysis for San Diego and Riverside counties, conventional production practices. http://coststudies.ucdavis.edu/
- Author: Gary Bender
Since our last article on high-density avocados appeared in Topics in Subtropics (Vol. 10 no. 1, Spring 2012) we have had a lot of questions from growers concerning the cost of installation of such a grove. We have also had a lot of interest from potential winegrape growers who think this might be the way to go given that wine-grapes use about 25% of the amount of water per acre compared to avocados. For higher quality wines growers use less water, but harvest lower pounds/acre.
I am currently advising a student at Cal State San Marcos who is doing a cost study for removing an avocado grove and installing a winegrape planting in San Diego County. Hopefully we will have an article on that in the near future.
We don’t have a lot of experience in high density avocados but we will try to show some costs to help you decide.
Clearing an older grove can get expensive. In a study we did in 2010 we found that it cost $40/tree to cut a tree down, haul the cut wood down to a firewood stack and haul to small branches to a chipper. The old stump is usually killed with a herbicide and left in place to rot. So, just to remove a tree at 109 trees/acre may cost $4,360 per acre.
For our high density planting we will be planting Hass avocados grafted on Dusa rootstock. We are using this rootstock because it appears from several trials to be a good rootstock for resistance to avocado root rot in the well-draining hillside soils in San Diego County.
The current price is about $30/tree (plus or minus). For a 10’ x 10’ spacing we would plant about 435 trees per acre, this would be an initial cost of $13,500/acre. We are not calculating the cost of a grove road installation, and we are assuming that the entire acre would be planted.
Planting cost: digging, planting, wrapping and staking trees takes about 15 minutes per tree. This includes carrying the tree to the hole. At 435 trees per acre, this would take about 109 hrs. At $14/hr, this would cost $1526/ac. Stakes (435) at $2.25/stake would cost $979/ac.
The irrigation system installation would cost $2,660/ac. This is based on an entire system being installed in a 20 acre block, divided by 20 to get the cost per acre.
There are quite a few other costs that you can see from our complete avocado cost study, but these basic costs will get the trees in the ground (Table 1).
Table 1. Basic costs per acre for the installation of a high density avocado grove. It is assumed that land is cleared and ready to plant. Installations of grove roads are not considered. |
|
Trees (Hass on Dusa rootstock) |
$13,500 |
Planting (digging, planting and wrapping) |
$1,526 |
Stakes |
$979 |
Irrigation system |
$2,660 |
Total per acre |
$18,665 |
If you are thinking about planting 10 acres, then you would need $186,650 in the bank to get the trees in the ground. There will be some shifting of costs because this study does not include clearing or building of grove roads, and with grove roads you will be planting less numbers of trees/acre.
Will you make more money in the long run? That is the question we are trying to answer with our high density trial in Valley Center.
Reference
Bender, G.S. and E. Takele. 2010. A guide to estimate compensation for loss of a single avocado tree. University of California Cooperative Extension county publication AV 606.
Takele, E., Bender, G.S., and M.Vue. 2011. Avocado sample establishment and production costs and profitability analysis for San Diego and Riverside counties, conventional production practices. http://coststudies.ucdavis.edu/
- Posted By: Chris M. Webb
- Written by: Ben Faber
Introduction
In numerous publications world-wide, planting hole recommendations for avocado and other subtropical crops are made for large holes from 2 feet by 2 by 2 to as much as a cubic yard. These recommendations also include incorporation of manures or composts comprising 25% by volume with the native soil. I have noted the use of large holes and amendments in several countries, including New Zealand, Guatemala, Brazil, Costa Rica, Mexico and the United States.
The various reasons given for making these large holes are to disrupt any compaction or limiting soil layers and to create a more conducive environment for root growth. In the case of replanting deciduous orchards, McKenry found it to be beneficial in actually replacing the native soil in the hole with pathogen free soil. In many cases, research has shown that holes much larger than the planting ball and using organic amendments can cause problems for many tree species. Improper mixing of the organic amendment can cause anaerobic conditions and settling due to amendment decomposition. Soil that has not been properly firmed in the hole can also lead to plant settling and stems can drop below grade leading to crown rot.
Nonetheless, on the basis of recommendations made in many countries there could be some value in these planting practices, especially in the light of the effect organic matter has on avocado root rot. Numerous studies have shown organic matter suppresses the causal agent of root rot. This study evaluated the effect of hole size and amendments on avocado growth in an ideal environment with excellent soil conditions and in a more harsh one with heavy soil texture and the presence of the root rot pathogen.
Materials and methods
On the north island of New Zealand in the Bay of Plenty, 20 trees each were planted to one of four treatments: a) small holes (12 by 18 inches) without amendment; b) small holes with 25% by volume compost; c) big holes (60 deep by 30 wide by 24 wide inches) without amendment and d) big holes with 25% by volume compost. Big holes were dug with a backhoe, while small holes were dug by shovel. Trees were approximately 2 feet tall at planting. Soil was a deep sandy loam at both sites. Trees were irrigated by drip irrigation. Trees were ‘Hass’ on ‘Zutano’ seedling rootstock. Trees were planted the second week of spring 2000. Tree height, trunk caliper and canopy volume were measured on a monthly basis for eight months and then twice a year for the next year. In Carpinteria, California a similar trial was established using ‘Hass’ on ‘Toro Canyon’ rootstock. Trees were approximately 2 feet tall at planting. The grove had a heavy clay loam soil and a history of root rot. The trees were on drip irrigation. The trees were planted summer 2001 and monitored for 18 months after planting.
Results and discussion
Figures 1and 2 show the results of the different planting treatments at sites in New Zealand on ideal soils and on the heavy soil infected with root rot in California. Only tree height is shown; trunk girth and canopy volume followed similar patterns. From planting onwards, there were no differences in tree growth in any of the treatments at any of the sites. This would lead one to the conclusion that there is no value in and a great expense in making big holes and incorporating amendment. This is especially so in hillside situations where moving equipment and amendments on steep slopes would be very difficult.
The trees at the Carpinteria site, although infested with root rot, all looked good. The addition of organic matter in conjunction with the clonal rootstocks did not apparently provide any greater disease resistance. This is in accordance with work done by John Menge which shows that the greatest benefit derived from mulching are seedling rootstocks. The effect of mulch on disease suppression diminishes with the rootstock’s resistance to root rot.
Figure 1. Tree height (meters) at site 1 in New Zealand 20 months after planting. No differences were found at the 5% level of significance.
Figure 2. Tree height (meters) in California 18 months after planting. No differences were found at the 5% level of significance.